Lumia 930 and Icon are not supported. Just as a reminder, Microsoft is supporting virtually every modern Lumia device with this build, but the Lumia 930 and Icon are excluded. They know what the issue is, and how to fix it, and I assume 930/Icon users will be onboarded by the time we see the next public build.

Lots of changes, still a freaking mess. Speaking generally, there is a ton of change in this build. But it is very much still a mess, with mismatched UIs that blend the old and the new. It’s particularly bad on the Lumia 1520, where many UI pieces—like the virtual keyboard—just don’t seem to “fit” correctly onscreen.

Project Spartan. Microsoft’s new web browser is here and working, but it’s not the default in this build yet. The address bar is at the top of the app, not the bottom where you can actually reach it, and Microsoft says it’s looking at changing that. Overall the, ahem, Spartan user experience—see what I did there?—works well on the phone form factor. Reading View is particularly nice.

Outlook Mail. While Microsoft basically hid the “Outlook” branding in Windows Phone 7.x/8.x—Mail, Calendar and People were in fact really Outlook Mobile apps—that branding makes a comeback in Windows 10 Mobile. (Curious side-bar: That is not the case in Windows 10 for PCs, where the Mail and Calendar apps lack the Outlook branding for some reason.) Anyway, I’ve always been a fan of the Mail app presentation on Windows Phone, but the new treatment in Outlook Mail is even better. It looks a lot like Outlook on other platforms and, curiously, like OneDrive as well. The only obvious thing missing is a two-pane view in landscape.

Outlook Calendar. Like Outlook Mail, Outlook Calendar gets a refreshing UI update, but only a few view styles are available at the moment (Day/Agenda).

People. This app has been updated but loses both the Outlook branding and the panorama user experience. Instead, we see a universal app-style pivot, which is pleasantly Windows Phone-esque, and the same contact bubbles you see in Messaging and elsewhere.

Phone. I don’t yet have this build on a SIM-capable phone, but in just rummaging around the Phone app I see a pretty convoluted UI, with a toolbar-like UI on both the top and bottom of the screen It’s ugly, and I hope this is updated.

Messaging. The text messaging app is likewise in a state of distress, but I like the little circle graphics for each person you’ve communicated with—they look like the sign-in graphic in the desktop version of Windows 10—and the conversation view is straightforward enough.

Maps. The Maps app has been updated to match the Maps app in Windows 10 for PCs, and I’m not surprised to see that it works well in this form factor too. This is one of the more successful universal apps in that it’s basically the same UX on any device. It works. (The Photos app is another good example of this.)

Switcher. As promised, the app switcher UI has been updated and now supports up to 15 apps on larger phones in a new grid format. Looks great.

I’ve received a lot of questions regarding using this build on daily use phones. I recommend against that, even with just a little bit of experience using it. The build is buggy, a visual mess, and incomplete. And certain problems in this build—there’s no Office, OneDrive backup of photos might break, and some networking features can’t be disabled—all indicate this isn’t for the faint of heart.

This is just a first peek. I’ll keep digging, and will install build 10051 on more phones as well.